1. Field of the Invention
The present invention relates to control of a boosting circuit which generates an internal power supply voltage in a semiconductor device.
2. Related Art
In a semiconductor device, a circuit for generating a desired voltage in the semiconductor device, a charge pump circuit is known. A semiconductor device such as a FLASH MEMORY includes two internal voltage generation circuits which operate in a normal operation state and a standby state to reduce a standby current.
An internal voltage generation circuit in the semiconductor device is for example disclosed in Reference 1* and Reference 2**. These patent documents disclose a boosting circuit comprising a charge pump circuit and a circuit for detecting an output voltage of the charge pump circuit to control an operation of the charge pump based on the detected output voltage. More specifically, the following technique is disclosed. That is, the boosting circuit detects an output voltage Vpp of the charge pump circuit, compares the output voltage Vpp with a reference voltage, activates the charge pump circuit when the output voltage Vpp is lower than the reference voltage, and inactivates the charge pump circuit when the output voltage Vpp reaches the reference voltage.
In the above boosting circuit, in order to reduce a current consumption in a standby state of the semiconductor device, it can be considered to reduce a DC current flowing in a circuit for controlling the operation of a charge pump circuit based on the output voltage of the charge pump in the standby state.
However, the response of the circuit is deteriorated when the DC current is reduced, resulting in a practical problem. In the standby state, while a rate of voltage drop caused by a leakage current or the like of a transistor in the semiconductor device is very low, the boosting rate of the voltage by the charge pump is considerably higher than that of the rate of voltage drop by the leakage current. For this reason, the low response of the boosting circuit also boosts a high voltage in the operation of the charge pump circuit, resulting in a large amount of ripple of a power supply voltage.
(References)
* Reference 1: Japanese Patent Laid-Open Publication No. 2001-95234 (see, for example, Paragraph [0007], FIGS. 12 and 13
** Reference 2: Japanese Patent Laid-Open Publication No. 2002-15571 (see, for example, FIGS. 1 to 3, Paragraphs [0043] and [0044])